Two areas of well exposed mid-crustal structures in the axial zone of the Pan-African Damaran orogenic belt show that basement has formed domes which have amoeboid forms on the scale of tens of km with steep sided overturned non-planar, non- cylindrical geometry. These are surrounded by open to tight synclinal cover envelopes that converge at depressions between the domes. The domes are found in association with a strong regional WSW moderately plunging lineation. Strain analysis demonstrates that domes have formed in a moderately plunging constrictional field. Structural features which normally indicate polyphase evolution such as mesoscale fold interference patterns are rare and inconsistent. Regional structural form, described morphogically by cylindrical domains, is defined by one fabric S0/S1. Secondary fabric trajectories and mesoscale fold oreintations are controlled by domain scale structure and not regional deformation trends. Dome formation is thus interpreted as being the result of a simultaneous flow and buckling episode within the middle crust. Deformation was extremely ductile. P-T estimates from thermobarometry with Grt-Bt, Grt-Crd-Bt-Sil assemblages indicate that peak metamorphic conditions during deformation were approximately 3.5kbar and 650°C in the cover envelopes and 7kbar 791°C in the basement domes, approaching the amphibolite-granulite transition. Interactive transpressional collision between three cratons during the latest Neoproterozoic-early Paleozoic: namely the Kalahari, Congo and Rio de la Plata caused constriction and extrusion in the Central Zone. The metamorphic gap between basement and cover occurred when the distance between regional isotherms was reduced by thinning at the basement-cover interface. Higher temperatures where preserved at dome cores. At the cooler margins of the Damara Belt thrust tectonics occurred, albeit obliquely with sinistral transpression. After dome formation granite intruded many domal structures.

The investigation covering 1500 square kilometres within the central granite zone of the Damara belt, South West Africa, revealed Pre - Damara (Abbabis) basement unconformably overlain by metasediments of the Damara Supergroup. The term Leeukop member is proposed for basal metaconglomerates of the Nosib Group that immediately overlie the basement augen-gneisses. Augen-gneiss clasts are present within the Leeukop metaconglomerates. The Damara orogeny has only partly affected the Abbabis rocks of the Tumas River Inlier but further to the west the Husab suite of red granites and granite-gneisses, as field and geochemical evidence suggest, were derived syntectonically during the Damara orogeny by reactivation of the pre- Damara basement. Rõssing alaskitic granites represent late stage melts, that were also derived from Pre- Damara basement rocks during orogenesis, which accumulated post-tectonically in structural traps at the base of the Khomas Subgroup. Salem granitoids are present in synclinal structures associated with metasediments of the Khomas Subgroup and syntectonic derivation by anatexis during the Damara orogeny is suggested. In the east the differentiated Gawib granitoid stock was emplaced post- tectonically through basement rocks into the Damara metasediments. A deep seated origin is indicated by high crystallisation temperatures (>8500°) obtained from quarternary Qz-An-Ab-Or- H₂0 plots. The metamorphic grade increases westwards from medium grade to high grade. In the east, the metapelites contain andalusite, and coexisting muscovite and quartz. This indicates that temperatures of 6000° at 3,5- 4 kb pressure were attained. In the west, coexisting wollastonite and anorthite in the Khan gneisses indicate pressure- temperature conditions of 720° at 4,5-5 kb. Two tectonic events were responsible for the regional structure. An early F₁ episode produced east- west oriented overturned folds and was followed by an intense F₂ episode of isoclinal folding which is responsible for the dominant northeast - southwest regional fabric. The interference of these folds in the proximity of the underlying basement produced the complex dome and basin structures seen in the central and western parts of the area. An F₃ episode of minor importance was also recognized. The presence of continental basement rocks in this central part of the Damara belt is evidence for formation of the orogen by in-situ deformation rather than continental collision.

This is an integrated study of the stratigraphy, deformation, magmatism, and metamorphism in the vicinity of the Ida and Palmenhorst Domes, an area in the southwestern Central Zone of the Damara Orogen, Namibia. The principal aim is to understand the timing of tectonic events through high-precision U-Pb dating of structurally constrained intrusions and anatectic rocks, and link these tectonic events across the Damara Orogen and Pan-African Orogeny. A secondary aim is to compare the Central Zone and Damara Orogen to other collisional orogens. The stratigraphy of the study area is similar to that noted elsewhere in the Central Zone, but the mapped distribution of lithologies differs slightly from previous work. Specifically, Damara Supergroup rocks have been found infolded with the Abbabis Complex, and the stratigraphic positions of certain units in have been locally reclassified. The mapped distribution of lithologies suggests a Type-2 fold interference pattern across the study area. This Type-2 fold interference is confirmed by structural analysis. A D2 deformation event formed strongly S- to SE-verging km-scale recumbent to shallow NW-dipping folds with smaller-scale parasitic folds. The long limbs of these folds are extended, and a number of shear zones are found on these extending limbs, as well as near the contact between the Abbabis Complex and the Damara Supergroup. NE-SW extension is associated with the late stages of D2, and forms a conjugate set of shear bands and a shallow NE-plunging mineral stretching lineation. This D2 event was overprinted by upright to steeply WNW-dipping km-scale D3 folds to form the domes in the study area. Mesoscale fold interference structures are rare, but D2 structures are shown to be consistently reoriented by D3 structures. D3 deformation does not have a strong vergence, and mesoscale D3 folds are rare. D2 and D3 were preceded by a D1 fabric forming event locally observed as rootless isoclinal intrafolial folds, and followed by brittle deformation. The Ida Dome is a fairly simple domal structure formed by the km-scale interference between a shallow NNW-dipping D2 anticline and an upright to steeply WNW-dipping D3 anticline. East of the Ida Dome, NE-trending D3 structures predominate, but are seen to overprint earlier D2 structures. The Palmenhorst Dome is a larger area where Damara Supergroup rocks have been infolded into the Abbabis Complex during D2 deformation. These isoclinal, N- to NW-dipping D2 folds have been refolded by upright D3 folds to form a Type-2 fold interference pattern. D2 structures along the southern margin of the Palmenhorst Dome dip steeply towards the south, in contrast to D2 structures elsewhere. This is interpreted to be the result of a lower-intensity km-scale D2 fold. The orogen-parallel extension and orogen-perpendicular recumbent folding that took place during D2 cannot be explained by previous structural models for the Central Zone and a new model is suggested where these structures form as the result of coeval irrotational NE-SW extension and S- to SE-verging simple shear during extensional collapse of the orogen. A number of intrusive rock types are found in the study area and have been dated using SHRIMP U-Pb. Amphibolite dykes have a chemical affinity to mafic rocks of the Goas Suite, and are suggested to be either pre-Damaran or early Damaran intrusives as they cut the gneisses of the Abbabis Complex, and are affected by D2. They have been dated at 2026.9 ± 2.3 Ma (zircon) or 557.2 ± 7.4 Ma (zircon) with metamorphic overgrowths in this sample giving 520 ± 6.9 Ma. Red, potassic granites emplaced near the contact with the Abbabis Complex and Damara Supergroup contain a D2 gneissic fabric and give ages of 536 ± 7.2 Ma (monazite), and zircons have lower intercept ages of 539 ± 17 Ma and upper intercept ages of 1013 ± 21 Ma. Grey granites are abundant in the study area, and form a continuum from dark grey granites (which are tonalitic to dioritic in composition and contain hornblende and abundant biotite) to light grey granites (which are leucogranitic and contain abundant K-feldspar and minor biotite). These grey granites show a fractionation trend from dark to light varieties, and cross-cutting relationships indicate that the lighter variety is younger than the darker variety. The grey granites show syn-D2 structural relationships and contain a fabric subparallel to the S2 fabric, and which is more pronounced in the darker varieties. They show similarities with granites described by earlier workers, and two samples have been dated at 519.1 ± 4.2 Ma and 520.4 ± 4.2 Ma (zircon). A variety of sheeted granites are found – quartz-feldspar-magnetite pegmatitic granites are associated with grey granites, occur axial-planar to F2 folds, and have metamict zircons which are dated at 530-525 Ma. Garnet (± cordierite) granites are leucocratic, have garnet poikiloblasts, are emplaced axial planar to F2 folds and are also folded and boudinaged by D2. They are associated with pelitic units in the Damara Supergroup and are dated at 520.3 ± 4.6 Ma (zircon) and 514.1 ± 3.1 Ma (monazite). Uraniferous leucogranites found are similar to those widely described in the Central Zone, but metamict zircons give imprecise ages of between 515 and 506 Ma. Pink pegmatitic leucogranites comprise pink perthitic feldspar and milky quartz, are emplaced into more brittle structures and gives an age of 434.4 ± 2 Ma (zircon). Almost all granites analysed appear to be crustal-melt granitoids, with the exception of the darker grey granites, which show a calc-alkaline affinity. No Salem-type granites are found in the study area. In addition, SHRIMP U-Pb analyses of zircons from three Abbabis Complex gneisses give ages of 2056 +11/-10 Ma, 2044 +32/-27 Ma and 2044 +17/-14 Ma, and titanites from an amphibolite sample give ages of 493.4 ± 6.4 Ma. Two anatectic leucosomes from D2 shear zones and shear bands give zircon ages of 511 ± 18 Ma and 508.4 ± 8.7 Ma in spite of high-U zircons. Lu-Hf data on zircons from an Abbabis Complex gneiss gives model ages of ca. 3 Ga, whilst similar data for a grey granite gives a model age of ca. 2 Ga. Zircons from the Abbabis Complex gneiss have variable O-isotopic values, whilst the grey granite gives O-isotopic values of ca. 7‰. These geochonological and isotopic data show that the Abbabis Complex is part of the Congo Craton, and that some amphibolites are pre-Damaran, whilst others may be related to the Goas Intrusive Suite, and represent a phase of early Damaran magmatism. In contrast to the chronology previously presented for the Central Zone, M1 in the study area appears to have occurred at 535-540 Ma, with M2 coeval with D2 deformation at 510-520 Ma. Elsewhere in the Central Zone, NW-verging D2 deformation is dated at 540-560 Ma, and the Central Zone appears to have a diachronous tectonometamorphic evolution along strike. It is suggested here that this represents the preservation of two separate tectonic events in the Central Zone at different crustal levels, one at 540-560 Ma and the other at 520-510 Ma. D3 deformation is suggested to have taken place at 508 Ma, immediately after D2 extension. The Central Zone began to cool following D2, and the 495 Ma titanite age reflects this cooling. Isotopic evidence from this and other studies shows that Damaran granitoids (with 1.5-2.2 Ga model ages) cannot be derived from the Abbabis Complex (with 3 Ga model ages) but must come from an alternative source, suggested here to be Kalahari Craton material subducted below the Congo Craton. Textural studies of a number of pelitic samples indicate syn-D2 low-pressure, high-temperature metamorphism. Differences in observed assemblages between various sample types are due to compositional differences, and samples appear to have reached similar conditions across the study area. Mineral compositional profiles show no prograde zoning, indicating mineral re-equilibration. Orthopyroxene is locally observed, suggesting lower-granulite conditions. This is confirmed by pseudosection modelling of a number of samples, which gives peak conditions of 750-850 °C and 4.5-5 kbar. This modelling shows lower-granulite facies conditions with higher temperatures than previous estimates based on mineral compositional geothermometers, which are affected by re-equilibration. These conditions are sufficiently high for fluid-absent biotite breakdown to form the voluminous anatectic leucosomes and granitoids in the southwestern Central Zone. Pseudosection modelling and phase relationships indicates a low-pressure (ca. 4 kbar) clockwise heating path, with slight decompression at the thermal peak. All metamorphism noted is 520-510 Ma M2 metamorphism, and no petrographic evidence exists for earlier 540-535 M1 metamorphism. This cryptic M1 is suggested to be related to the emplacement of the Goas Intrusive Suite and Salem-type granites early in the orogenic history, whilst M2 may be related to thermal relaxation following crustal thickening early in the orogenic history, but requires an additional heat source. The difference in ages for deformation and metamorphism between the study area and elsewhere in the lower grade portions of the Central Zone is suggested to be related to the preservation of different portions of the orogenic history in different areas. The results of this study together with previous work details a multi-stage evolution for the Central Zone involving subduction, continent-continent collision, crustal thickening, slab breakoff, magmatism, granulite-facies metamorphism and exhumation of the mid-crust. This multistage evolution explains the multiple ages for deformation and metamorphism in the Central Zone. NW-folding and thrusting documented in the Karibib area at 560-540 Ma is related to an early phase of crustal thickening owing to continent-continent collision following a brief period of subduction. Slab breakoff led to asthenospheric upwelling and heating of the lower crust, and produced the Goas Intrusive Suite and Salem-type granites, as well as providing heat for 540-535 Ma M1 metamorphism and the melting of the crust to produce anatectic red granites. SE-verging deformation, extension and granulite facies metamorphism recorded in this study is related to orogenic collapse following crustal thickening, and the heat source for low-P, high-T metamorphism may be highly radiogenic crust that was thickened , which is suggested to be either burial of crust enriched in heat-producing elements, or asthenospheric upwelling owing to delamination of the Congo Craton lithospheric mantle or asthenospheric upwelling owing to the position of the southwestern Central Zone on a major orocline. The events recorded for the Central Zone have been correlated across the entire Damara Orogen, and the timing of events can be correlated along strike into the Zambezi Belt. Events in the Kaoko Belt appear to predate those in the Damara Belt, which appears to also show a similar collisional timing to the Gariep Belt. It is therefore proposed that the Gariep and Damara Belts formed part of a younger orogenic episode to that which formed the Kaoko and Dom Feliciano orogenic belts. The Damara Belt shows similarities to both Alpine-style and Himalayan-style orogens. An evaluation is provided of a channel flow model for the Central Zone, but there are currently insufficient data for the Damara Belt to confirm or repudiate this model. Nonetheless, this study has identified a more complex tectonic history for the Central Zone than previously, with chronological and lithogeochemical evidence for two episodes of deformation and metamorphism that have been linked to the collisional history of the entire Damara Belt and have been correlated with events in other Pan-African belts.

The Zerrissene turbidite system of central-western Namibia is a late Proterozoic sequence which consists of dominantly siliciclastic turbidites interbedded with minor turbiditic and hemipelagic marbles. The basin in which these sediments were deposited is located at the junction of the coastal and intra-cratonic arms of the Pan-African Damara Orogen, and an understanding of the sedimentary evolution of this basin is therefore important to the understanding of the development of the orogen as a whole. One major and two minor phases of folding have deformed the sediments, but the grade of metamorphism is low and sedimentary structures are often well preserved. Further, the area lies entirely within the Namib Desert and the lack of vegetation cover results in good outcrops providing an unusual opportunity for examining a large Precambrian turbidite system. The system consists of five formations: three siliciclastic and two mixed carbonatesiliciclastic units. The floor of the system is not exposed, and the oldest sedimentary rocks which outcrop are siliciclastics of the Zebrapiits Formation. This is overlain successively by the Brandberg West Formation (dominantly calcareous), the Brak River Formation (siliciclastic), the Gemsbok River Formation (calcareous) and the Amis River Formation (siliciclastic). Nine silicilastic turbidite facies have been recognised in the basin. These are facies A₂ (disorganised onglomerates), B₁ (horizontally laminated to massive greyackes), C₂ ("classical" turbidites), Dl (sandstone-shale couplets with base cut-out Bouma sequences), D₂ (sandstone-shale couplets with less sand than shale and base cut-out Bouma sequences), E (coarse, discontinuous sandstone-shale couplets), F (slumped units), G (shale) and H (glacial dropstones). Four facies are associated with the carbonate horizons, and these carbonate facies are given the suffix c to distinguish them from similar siliciclastic facies. These are facies Ac (disorganised and graded marble breccias), facies Cc (graded carbonates), facies Gc (hemi-pelagic marbles) and facies G (pelagic shales). The basal Zebrapiits Formation is made up of relatively thin packages of thin- to thickbedded, laterally continuous facies D₁, D₂ and B₁ beds encased in thick envelopes of shale. This type of sequence is typical of a distal lobe-fringe, and requires an unconfined basin-floor on which it can develop. The overlying Brandberg West Formation consists of a basal portion of interbedded facies Cc and G, followed by a sequence dominanted by facies Gc. This sequence is interpreted as representing outer-apron carbonate turbidites, derived from multiple point sources (facies Cc), with background pelagic settling (facies G) overlain by hemi-pelagic deposits (facies Gc). A reversal back to siliciclastic turbidites followed with deposition of the Brak River Formation. This sequence comprises relatively thick packages of laterally continuous facies B₁, D₁, and D₂ beds sandwiched between facies G shales, a succession characteristic of a lobe to lobe-fringe environment with intermittent abandonment of lobes. An unconfined basin floor adjacent to a passive margin is required for the development of this type of sequence. Glacial dropstones (facies H) are found in the upper portions of this formation, and slumped beds are also present (facies F), but are uncommon. The facies F beds are only found in association with facies H and are therefore considered to be genetically related. Slumping of beds was possibly caused by an oversupply of sediment from ice-rafting which caused instability. The overlying Gemsbok River Formation has a sequence similar to the Brandberg West Formation in that the basal portion consists of interbedded facies Cc and G, which is overlain by a thick sequence of largely facies Gc beds. Minor facies Ac beds occur near the top of the overall sequence. This formation is interpreted as an outer-apron succession with the facies Ac beds representing distal inner-apron deposits, indicating progradation of the system. The youngest unit in the basin, the Amis River Formation, shows strong lateral variation from west to east. In the west the sequence comprises laterally continuous facies B₁, C₂, D₁ and D₂ with rare, discontinuous facies E beds. Facies G is relatively minor in the sequence. In the east the succession is dominated by facies D₁, D₂ and G, and this succession is interpreted as a sequence of distal turbidites which were deposited on a basin-plain. The system developed by aggradation rather than progradation as only minor cycles are developed. Geochemical and petrological features indicate that the entire siliciclastic system was derived from a granite-recycled orogen terrane. Palaeocurrent data are unreliable because of the deformation, but transport was initially from the south-west, moving later to the west and north-west. The provenance of the carbonates is uncertain as reliable palaeocurrent indicators are rare, but they could have been derived either from South America or from the extensive carbonate deposits developed on the north-western margins of the basin. The Zenissene siliciclastic turbidite system represents the distal portion of a major submarine turbidite system, the more proximal parts of which now lie west of the exposed basin, either under the Atlantic Ocean or in eastern South America. The calcareous deposits developed as an apron adjacent to a multiple point source, the position of which is at present unknown.

The Matchless Amphibolite Belt (Damara Orogen, Namibia) hosts several volcanogenic-exhalative, sediment-hosted stratiform cupriferous pyrite deposits. These are thought to be related to submarine volcanism during the early evolutionary stages of a narrow Damaran ocean, the Matchless Trough. The mineralized bodies examined (Ongeama, Ongombo and Matchless West Extension) are deformed and metamorphosed to low-medium grade (greenschist-amphibolite facies). They are associated with metapelite and amphibolite country rocks, and crop out as prominent limonite-rich gossans. The elongated shape of the sulphide bodies suggests a structural control. The mineralization normally consists of a variably developed massive sulphide portion, either quartz-, talc- or amphibole-bearing, and a stratigraphically overlying, extensive horizon of sulphide- and baryte-bearing exhalite (magnetite quartzite and less common talc- and actinolite-bearing schists). Lateral and vertical mineralogical changes within the mineralization match with significant variations in the element distribution. A metamorphosed and deformed alteration pipe, indicating the position of the fluid conduit, can be recognized in association with some ore bodies. The formation of quartz-muscovite and chlorite alteration envelopes (Ongeama, Matchless West Extension) and the presence of subtle mineralogical changes (Ongombo) in the immediate wallrocks, accompanied by extensive redistribution, leaching and introduction of elements from outside, suggest the hydrothermal metasomatic origin of the alteration zones. Element zoning within the mineralized bodies can be related to the original position of the vent, possibly coinciding with the intersection of the axis of the alteration pipe with the sulphide body. Cu, Zn, Au (pro parte) and Mo are enriched proximal to the vent, whereas Pb, Ba, Mn, Ag, Au, Sn, Bi and W enrichment characterizes the distal facies of the mineralization. In spite of the obliterating and disrupting effects of the regional dynamo-metamorphism, the element distribution within the mineralization and alteration zones examined is comparable with the geochemical trends observed in present-day mineralizing systems in early- stage oceanic environments (e.g. Guaymas Basin). During exploration for blind volcanogenic mineralization, the detection of hydrothermally altered rocks is fundamental in indicating the proximity to the mineralization. The localization of the alteration zone is also important in the interpretation of the regional geology of the explored area: in deformed terrains the assessment of the stratigraphic position of the alteration zone, relative to the mineralization, helps in establishing the polarity of the sequence.

After the establishment of the N-S Andib-Ganamub trough, the ubiquitous Lower Nosib subarkose was succeeded in the west by the Upper Nosib greywacke which indicates that orthogeosynclinal subsidence was already active in pre-Damara times. A pulse of NNE folding (F₁N) concluded this sedinentary cycle and was accompanied by amphibolite-grade metamorphism (M₁), occasional migmatisation (A₁), and later feldspar blastesis. This episode was most intense in the west, so that the overlying Damara rocks paraconformable in the east, are unconformable there. Martin's (1965) separation of the succeeding Damara basin into a western eugeosyncline and an eastern miogeosyncline applies very well to this area, though the separating hinge-line appears to have been located farther to the west (±80 Km) of the Kamanjab inlier, along the western flank of a N-S geanticlinal belt. The Lower Bakos semipelite and lenticular carbonate, thinning out against the eastern flank of this positive element controlling the deposition, may, prior to deformation, have created a transition between the western eugeosynclinal greywacke and the eastern miogeosynclinal Lower Otari carbonates. The fractured hinge-zone provided channels for the ascent of syndepositional intrusions and volcanics. Regional erosion following upwarping in the east caused a large influx of detritus into the Khomas furrow prior to the disconformable deposition of the Tillite Substage, which is the only reliable chronostratigraphic link between the base of the Upper Otavi and that of the Upper Bakos Series, the latter partially intertongueing with the succeeding Khomas Series. Gravitational creeping of the miogeosynclinal carbonates down the western slope of the upwarped Kamanjab inlier towards the sinking basin, produced the first folding (F₂O) in the east. Almost contemporaneously, buoyant uplifting forces, related to anatexis (A₂) along the axis of the eugeosyncline, created slopes sufficient to convey nappes (F₂S) of scarcely metamorphosed Damara schists towards the eastern foreland, overriding the miogeosyncline along the N-S Sesfontein Thrust. Eastern foredeeps were rapidly filled by the Mulden molasse. Steep slip folding (F₂S and F₄) in the cores and roots, and the formation of scattered domes at depth, controlled the successive structural evolution of the nappes. Large-scale axial undulations were later produced by orthogonally superposed F₃ folds striking east. The Damaran metamorphism (M₂ ), which outlasted deformation, has a Barrovian character and grades in the Damara sediments from amphibolite (sillimanite) grade in the west to greenschist (sericite- chlorite) grade in the east. In the previously dehydrated, deformed and metamorphosed, polymetamorphic (M₁/M₂ ) Nosib terrains, retrograde parageneses and transition granulites developed to the east and to the west of the Damaran hornblende-oligoclase isograd respectively. The Damaran tectono-thermal episode culminated in advanced migmatisation of the Khomas greywacke (possibly equivalent to the Salem granite-gneiss) and final anatexis (A₂ ) in the late-kinematic Ganias -Uhima (possibly equivalent to the Donkerhoek) granite, followed by widespread feldspar blastesis. The drop in rheomorphism in the deformed mass at the margin of the migmatite zone induced intense shearing and produced belts of mylonite and cataclastic gneiss. At a later stage, the Sesfontein Thrust was buffered against the Otavi dolomite relief and its speed of advancement reduced to match that of the erosion of its frontal toe, which now separates two completely different structural-stratigraphic domains: i) an eastern miogeosynclinal, feebly metamorphosed and volcanic-free domain (Damara System, Outjo Facies) deformed into non-basement-involving tectonites, overridden by ii) a western domain of suprastructural nappes and metamorphosed eugeosynclinal sediments (Damara System, Swakop Facies) deformed in response to basementinvolving tectonic processes promoted by deeply seated anatexis along the axis of the former eugeosyncline. The present model involves many stratigraphic revisions, one of the most important being that no rocks older than the Nosib Formation outcrop in the area and possibly along most of the Damara mobile belt in the western Kaokoveld.

Thesis (MSc)--Stellenbosch University, 2005. / ENGLISH ABSTRACT: The northeast-trending south Central Zone (sCZ) of the Pan-African Damara belt in central Namibia is structurally characterized by kilometer-scale, northeast-trending dome structures developed in Neoproterozoic rocks of the Damara Sequence. A number of different structural models have been proposed for the formation of these domes in the literature. This study describes the structural geology of the Usakos dome. The study discusses the structural evolution of the dome within the regional framework of the cSZ that represents the high-grade metamorphic axis of the Damara Belt, characterized by voluminous Pan-African granitoids. The northeastern part of the Usakos dome is developed as an upright- to northwestverging anticlinorium containing a steep southeasterly-dipping axial planar foliation. The northeast fold trend persists into the southwestern parts of the Usakos dome. However, this southwestern core of the dome is inundated by synkinematic granitic sheets. Distinct marker horizons of the Damara Sequence outcrop as screens within the granite, preserving a ghost stratigraphy. These screens illustrate the position and orientation of second-order folds. Significantly, most of the stratigraphy of the Damara Sequence is overturned in these folds. For example, some second-order anticlines developed in the northeastern parts of the Usakos dome can be followed along their axial traces into the southwestern hinge of the dome, where they appear as synformal anticlines, i.e. synformal structures cored by older strata, plunging towards the northeast. The inverted stratigraphy and northeasterly fold plunges suggest the northeast-trending folds are refolded by second-generation, northwest-trending folds, thus, forming kilometer-scale Type-2 interference folds. The resulting fold geometries are strongly non-cylindrical, approaching southwest-closing sheath folds indicating a top-to-the-southwest material transport. Lower-order folds in this overturned domain show radial fold plunges, plunging away from the centre of the dome core, as well as a shallowly-dipping schistosity. The close spatial and temporal relationship between granite intrusion and the formation of the southwest-vergent, sheath-type folds, radial distribution of fold plunges and the subhorizontal foliation confined to the southwestern hinge of the Usakos dome are interpreted to signify the rheological weakening and ensuing collapse of the developing first-order Usakos dome immediately above the synkinematic granite intrusions. Orogenparallel, southwest-vergent sheath folds and top-to-the southwest extrusion of the southwestern parts of the Usakos dome and northwest-vergent folding and thrusting characterizing the northeastern extent of the Usakos dome are both responses to the northwest-southeast- directed contractional tectonics recorded during the main collisional phase in the Damara belt. On a regional scale, the Usakos dome represents the link between the foreland-vergent northeastern part of the sCZ and the southwest-vergent, high-grade southwestern parts of the sCZ. The results of this study illustrate how dramatic variations in structural styles may be caused by the localized and transient rheological weakening of the crust during plutonic activity. / AFRIKAANSE OPSOMMING: Die noordoos-strekkende, suidelike Sentrale Sone (sSS) van die Pan-Afrikaanse Damara gordel in sentraal Namibië word karakteriseer deur kilometer-skaal, noordoosstrekkende koepel strukture, ontwikkel in die Neoproterozoïkum gesteentes van die Damara Opeenvolging. 'n Aantal verskillende struktuur modelle is voorgestel in die literatuur vir die vorming van hierdie koepels. Hierdie ondersoek beskryf die struktuur geologie van die Usakos koepel. Die ondersoek bespreek die strukturele ontwikkeling van die koepel in die regionale konteks van die sSS, wat die hoë graadse metamorfe magmatiese as van die Damara Gordel verteenwoordig, en karakteriseer word deur omvangryke Pan-Afrikaanse granitoïede. Die noordoostelike gedeelte van die Usakos koepel is ontwikkel as 'n antiklinorium met 'n vertikale- tot noordwestelike kantelrigting. wat 'n steil hellende, suidoostelike asvlak planêre foliasie bevat. Die noordoos-strekkende plooiing kom voor tot in die suidwestelike kern van die Usakos wat ingedring is deur sinkinematiese granitiese plate. Die posisie en oriëntasie van tweede-orde plooie is afgebeeld in die graniete deur 'n skimstratigrafie wat preserveer is deur duidelike merker horisonne van die Damara Opeenvolging. Die stratigrafie van die Damara Opeenvolging is opmerklik meestal omgekeer in hierdie plooie. Byvoorbeeld, tweede-orde antikliene ontwikkel in die noordoostelike gedeelte van die Usakos koepel kan gevolg word langs hul asvlakspore tot in die suidwestelike skarnier van die koepel, waar dit voorkom as sinforme antikliene, d.w.s. sinforme strukture met ouer strata in die kern wat na die noordooste duik. Die omgekeerde stratigrafie en noordoostelike plooi duiking impliseer dat die noordoosstrekkende plooie weer geplooi is deur tweede-generasie, noordwes-strekkende plooie, wat dus aanleiding gegee het tot die vorming van kilometer-skaal, tipe-2 interferensie plooie. Die gevolglike plooi geometrieë is uitdruklik nie-silindries, en toon 'n oorgang na skede plooie met 'n sluiting na die suidweste, wat dui op 'n bokant-na-die-suidweste materiaal vervoer. Laer-orde plooie in die omgekeerde domein vertoon radiale duiking van die plooie, weg van die middelpunt van die koepel kern, sowel as 'n vlak hellende skistositeit. Die noue ruimtelike en temporele verwantskap tussen graniet intrusie en die vorming van skede-tipe plooie met 'n kantelrigting na die suidweste, die radiale verspreiding van plooi duiking, en die subhorisontale foliasie wat beperk is tot die suidwestelike skarnier van die Usakos koepel, word interpreteer as 'n aanduiding van die reologiese verswakking en die gevolglike ineenstorting van die ontwikkelende eerste-orde Usakos koepel, onmiddellik aan die bokant van die sinkinematiese graniet intrusies. Die orogeenparalleie skede plooie met kantelrigting na die suidweste en bokant-na-die-suidweste ekstrusie van die suidwestelike gedeelte van die Usakos koepel, en plooiing met kantelrigting na die noordweste en stootverskuiwing wat kenmerkend is van die noordoostelike gedeelte van die Usakos koepel, is beide 'n reaksie op die noordwessuidoos- gerigte vernouings tektoniek opgeteken gedurende die hoof botsings fase in die Damara gordel. Op 'n regionale skaal verteenwoordig die Usakos koepel die verbinding tussen die noordoostelike gedeelte van die sSS met 'n voorland kantelrigting. en die hoë graad suidwestelike gedeelte van die sSS met 'n kantelrigting na die suidweste. Die resultate van hierdie ondersoek toon aan hoe dramatiese variasies in struktuur style veroorsaak kan word deur die gelokaliseerde en kortstondige reologiese verswakking van die kors gedurende plutoniese aktiwiteit.

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A thesis submitted to the Faculty of Science in fulfilment of the requirements for the degree of Doctor of Philosophy at the School of Geosciences University of the Witwatersrand, Johannesburg, 2017 / Namibia, the 6th largest producer of uranium globally, has produced uranium from Pan African granite-hosted (primary) deposits since 1976, and from palaeochannel deposits since 2007; exporting 3 472 tonnes U in 2016. The large granite-hosted deposits at the Husab Mine are expected to add over 5 700 tonnes U/year at peak, while three large primary-hosted deposits remain in various stages of development at Goanikontes, the Ida Dome, and Valencia. This study presents a comprehensive geological, geochemical and uranium mineralogical appraisal of four of the major primary-hosted uranium deposits, all situated within the southern Central Zone (sCZ) of the polydeformational (D1-D3) Damara Belt. The sCZ comprises highly deformed Neoproterozoic sediments, unconformably draped over rheologically competent granite-gneiss domes and inliers of a Palaeoproterozoic basement. A suite of fractionated sheeted leucogranites (SLGs) are a characteristic of the final stages of Orogenic deformation; while most SLGs appear to precede D3 deformation and metamorphism (ca. 510 Ma); most of the mineralised SLGs across the region invade reduced-facies sediments in pressure shadows formed in the hinges and limbs of upright D3 antiforms, proximal to basement inliers. A pre-existing, six-fold, alphabetised SLG classification scheme is revised and extended to categorise distinctive and consistent field and petrographic characteristics of the SLGs across the region. Discriminating SLG sub-types is less consistent in standard geochemical diagrams, except where high field-strength (HFS) and rare-earth elements (REE) are concerned. REE profiles in pre-D3 SLGs reflect abundances, or paucities, of characteristic accessory mineral assemblages; while REE profiles show relative REE enrichment, prominent REEfractionation and -ve Eu anomalies in the uraniferous SLGs, reflecting lower-percentage partial melts in the more uraniferous samples. The overwhelming majority of primary uranium mineralisation is in magmatic uraninite, followed by coffinite which predominate as a replacement phase of uraninite, and more rarely as solid solution with thorite. The refractory minerals betafite and brannerite are rare, but are locally abundant in discrete, magmatic textures within uraniferous SLGs of some deposits. Hydrated uranyl silicates predominate in the supergene portions of the orebodies across the region. An electron microprobe study presents the first comprehensive assessment of uraninite compositions in the region, while Husab deposit betafite and brannerite compositions allow for a well-rounded comparison with refractory minerals from the Rössing deposits. Key Words Primary Uranium, Granite, Orogenic, Damara, Namibia, Rare Earth Elements, Mineralisation, Fractionation, High-grade Metamorphism, Economic Geology, Mining, Processing, Uraninite, Coffinite, Etango, Goanikontes, Husab, Ida Dome, Rössing, Valencia / XL2018

A brief account of the location and physical aspects of the region is followed by descriptions of mapping and laboratory techniques employed. Recent ideas on regional stratigraphical correlation in South West Africa are critically reviewed. Strata lying southeast of the farm Losberg 105 have, on the basis of lithology and copper mineralisation, been correlated with the Tsumis Formation. The Hasib Formation, of predominantly marine character, has on structural grounds been excluded from the Damara System. The latter here has a greater thickness than elsewhere in South West Africa, unless isoclinal folding is much more prevalent than has been assumed. The occurrence on Eintracht 118 of a pebble conglomerate, tentatively equated with the Chuos Tillite, makes possible a subdivision of the Damara strata into the various series established in the literature. It has been found possible to differentiate between Kamtsas and Damara quartzites on petrological grounds. Further, it is concluded that the bulk of Hakos carbonate rocks originated as dolomites and have subsequently been dedolomitized to a greater or lesser extent. The area contains both ortho- and para-amphibolites, as well as one occurrence of intrusive granite. Evidence is given for at least three periods of deformation. It is oonsidered that, if the Hosib Formation was involved in a pre-Damara orogenic episode, later folding must have been co-axial with this. Sedimentation and metamorphism are treated in broad outline. There appears to have been a deepening of the basin of deposition from Hasib to Damara times. Cyclicity in sedimentation is evidenced by lithological associations in the Damara strata. The entire area falls into the greenschist facies of regional metamorphism. Superficial deposits include river gravel and, silt, quartzite- and vein quartz-rubble, calcrete and Kalahari sand. The economic geology is described with special reference to the widespread copper mineralisation.